PCT: Cajon Pass to Agua Dulce Trail is a 221.7 mile lightly trafficked out and back trail located near Phelan, CA that features beautiful wild flowers and is rated as difficult. The trail offers a number of activity options and is accessible from March until November. Horses are also able to use this trail.
I have not done this whole section but I like the stretch between Guffy Campground and Inspiration Point for altitude training and it's beauty. It's 7000" to 8500", the highest being on the east end but a lot of up and down in between, staying for the most part on Blue Ridge itself or very near it so the views to the north and south are really nice. The oaks and chaparral on the west end quickly give way to open jeffrey/ponderosa forest with white fir and a few cedars. There is NO water between Interstate 15 and Grassy Hollow unless you scramble down the steep Acorn Trail to Wrightwood. Blue Ridge Campground is roughly halfway between Inspiration Point and Guffy. There's only light use in the winter because the gate is locked to vehicle traffic at Inspiration Point until the Mountain High Ski Resort closes down for the season. If you like thin air this is a nice 10 mile out and back. I'm posting a few pics.